1. Field of the Invention
The present invention relates to a drum rotating device which is arranged to rotate a drum with a motor mounted in the drum.
2. Description of the Related Art
Devices for rotating a cylindrical drum with a motor mounted in the drum in order to improve the space efficiency are known in the art. As examples of a conventional drum rotating device, JP 5086787 (A) discloses a device for raising/lowering a roller shade and JP 11336453 (A) discloses a shutter device. Both of these are drum rotating devices using a driving device mounted in the drum for rotating the drum. The driving devices include a motor and a decelerator for decelerating the rotating output of the motor. The output shaft of the decelerator is linked to the drum to rotate the drum. The drum rotating devices also include a supporting arrangement, such as a bracket, for supporting the driving device at a nearby fixed portion, and other supporting arrangements on both sides of the drum for supporting the drum itself to be freely rotatable relative to the fixed portion.
Yet another exemplary conventional drum rotating device is disclosed in JP 2008517576 (T), which includes a driving device placed in a guide roller fixed to a frame. The driving device includes a motor and a transmission portion. The driving shaft of the transmission portion is linked to a drum arranged about the outer periphery of the guide roller. The drum is held on the outer periphery of the guide roller coaxially therewith a circular arc guide block fixed to the inner wall of the drum. The drum is rotated relative to the guide roller by sliding movement of the guide block on the outer peripheral surface of the guide roller.
The drum rotating devices disclosed in JP 5086787 (A) and JP 11336453 (A), however, have a complicated structure because supporting arrangements are separately provided, one of which supports the driving device mounted in the drum and the other that supports the drum such that the drum can rotate. Moreover, the center of rotation of the drum may be located offset with respect to the center of the output shaft of the decelerator rather than in line with the center of the output shaft. If they are offset relative to each other, the drum cannot be rotated stably.
In the drum rotating device of JP 2008517576 (T), one end of the drum is arranged to slide on the outer periphery of the guide roller within which the motor is mounted, thereby ensuring coaxiality. However, the other end of the drum is supported at its shaft by another frame. Therefore, in a case of low positional accuracy of the drum shaft at the other end, the axis of rotation of the drum may be offset with respect to the driving shaft rather than in line with the center of the output shaft to thereby cause an unstable rotation of the drum.